Williams spent most of this season as a free agent before signing with the Baltimore Ravens in November. The 37-year-old played in seven games for the team, including its 17-3 loss to the Buffalo Bills in the AFC Divisional Round.
After Baltimore's season ended, it released him Jan. 18.
The Packers announced on Thursday they signed Williams to their practice squad. He played the first eight seasons of his career in Green Bay from 2007 to 2014, winning a Super Bowl with the organization and making the Pro Bowl in 2010. He also played with the team in 2018 and 2019.
This marks the second time a player has had a chance to play in two playoff games for two different teams. Offensive tackle Jared Veldheer signed with the Packers on Jan. 12, three days after he started the Indianapolis Colts' AFC Wild Card Game loss to the Bills.
Green Bay will host the Tampa Bay Buccaneers on Sunday at 3:05 p.m. ET, with the winner advancing to Super Bowl LV.